This invention relates to a power generation system which extracts useful power from water waves. In particular, the invention relates to the interaction of various elements of the design of a wave driven generator unit. More specifically, the present invention absorbs wave energy, converts that energy into electrical energy, and transports that electrical energy from its offshore point of generation to a land-based power grid. Thus, the present invention produces large quantities of power economically for a public utility or large industrial user.
Methods and apparatus designed to capture and convert wave energy into a variety of other forms of useful energy are described in a number of prior art publications and patents. See, for example, U.S. Pat. Nos. 562,317, 632,139, 694,242, 738,996, 882,883, and 917,411. These early patents relied on mechanical linkages between fixed floats to trap the rocking, lifting, falling, or longitudinal motion of the waves but were highly inefficient due to their mechanical complexities. Some of the most mechanically complex devices are illustrated in U.S. Pat. Nos. 1,169,356, 1,471,222, 1,528,165, 1,818,066.
A study of the prior art shows that most inventions designed to convert wave energy into useful energy utilize either (1) the kinetic energy of the waves by devices such as paddle wheels, or (2) the wave's potential energy by a float or a series of floats. Examples of inventions which rely upon kinetic energy are disclosed in U.S. Pat. Nos. 1,072,272, 4,152,895 and 4,208,875. The vast majority of prior art inventions for converting wave energy into useful energy rely upon the potential energy of a wave, i.e., the lifting power of the wave. Many such inventions rely upon a single float for absorbing a wave's energy. See, for example, U.S. Pat. Nos. 562,317, 738,996, 1,202,742, 1,471,222, 1,647,025, 1,746,613, 1,953,285, 1,962,047, and 3,487,228. Other early inventions rely upon a series of floats for converting the wave's potential energy into other forms, examples of which include U.S. Pat. Nos. 632,139, 855,258, 882,883, 917,411, 1,408,094, 1,567,470, 1,688,032, 1,867,780, and 1,925,742.
U.S. Pat. No. Re. 31,111 relates to wave driven generators comprising a plurality of floats that are tuned to be responsive to incoming waves by the use of different sized floats whereby wave energy is extracted by the floats and converted into hydraulic energy. This hydraulic energy is then employed to drive a turbine generator and generate electricity. The floats are connected together by hinges as to form what is defined as a "Hagen" array. Each float is pivotally connected to a larger float in such a manner as to allow relative movement between the floats. Hydraulic pistons and cylinders are mounted between the floats. These hydraulic pistons and cylinders are responsive to the relative movement between the hinged floats, and generate hydraulic energy in response to such movement. This hydraulic energy is stored in an accumulator which is then converted into electrical energy by a turbine-generator, located onboard of one of the floats. The array is moored to the sea floor by cables in a manner such that it is free to rotate so the floats maintain a desired position, i.e. facing the incoming waves.
A conceptual presentation of a wave energy conversion system appears in Transactions of the ASME, page 492, Vol. 105, December 1984. The system depicted therein includes an array, composed of rafts or floats of various lengths hinged together, and hydraulic pistons and cylinders positioned between the floats for absorbing wave energy and converting it into electrical energy. An articulated raft system, or array, is shown moored to the sea floor by a single anchor leg mooring system. A schematic representation of an onboard power conversion system is illustrated with the components of the system including hydraulic pistons and cylinders, accmulators, turbines, and generators. A submarine cable is illustrated for transmitting the electrical energy that is generated.
The Hagen-array system of hinged rafts suffers from the fact that the unit length of the rafts perpendicular to the crests (parallel to the line of incidence) must be approximately one wave length of the incident waves. The result is good efficiency relative to the beam dimension of the rafts but poor efficiency in terms of energy extracted per raft size or weight. The poor efficiency results because the Hagen-array system does not make use of the physical parameters of the rafts other than unit length to tune the system properly so as to respond to the broad spectrum of wave frequencies that occur in the ocean.
A number of patents disclose utilizing a plurality of floats to convert wave energy into useful energy. For example U.S. Pat. Nos. 4,392,349, 4,098,084, 3,879,950, and 1,408,094 disclose raft-like floats, hinged together, so as to form articulated chains or arrays. U.S. Pat. Nos. 4,241,579, 4,073,142, 4,048,801, 1,757,166 disclose energy conversion systems where a plurality of buoy-like floats are positioned in particular patterns so that wave energy resulting in upward and downward reciprocation of the floats is converted into useful energy. U.S. Pat. No. 3,758,788 discloses an energy conversion system where buoyant structures are connected together by pivotal structures and bellows which are activated by movement between the buoyant structures. The positive air or fluid pressure is then used to drive a turbine generator to generate electrical energy. A variety of hinges are disclosed for connecting rafts or floats together. For example, see U.S. Pat. Nos. 4,098,084, 3,879,950, 1,408,094, 917,411, 882,883, and 632,139. Additionally, U.S. Pat. No. 4,118,932 discloses hinging two floats together whereby the hinge also forms a pump which generates hydraulic energy in response to the relative rotational movement of the floats about the hingeline. Other prior art patents disclose a variety of pistons or bellows to convert wave energy into hydraulic energy, such as U.S. Pat. Nos. 4,408,454, 4,208,875, 4,013,382, 3,879,950, 1,757,166. Additionally, the device known as the Salter "nodding duck" which is disclosed in U.S. Pat. No. 3,928,967 utilizes a variable stroke rotary pump to convert the pivotal motion of its energy removing member into usable hydraulic energy.
U.S. Pat. No. 3,928,967 describes a system composed of a plurality of wave power absorbers deployed so as to intercept power from a line parallel to the incident wave crests that is long compared to the dimension perpendicular to the wave crests. The device described in this patent is an efficient absorber but suffers from the lack of stable reference necessary for power extraction. Although the device incorporates several features that improve the efficiency of energy capture, the concept fails to incorporate the more important features necessary for economical wave energy generation efficiency.
A number of other mooring or anchoring means are disclosed in the prior art. See, for example, U.S. Pat. Nos. 4,408,454, 4,013,382, 3,879,950, 1,746,613, 917,411 and 855,258. The supporting structure or mooring system required to operate many of these inventions, however, is quite elaborate and costly. See, for example, U.S. Pat. Nos. 1,757,166, 3,879,950, 3,928,967, 4,013,382. A number of prior art patents disclose converting the captured wave energy into electrical energy. See for example, U.S. Pat. Nos. 4,152,895, 4,013,382, 3,879,950, 3,487,228, 1,962,047, 1,757,166 and 738,996.
The prior art is limited either to the mechanism by which power is transferred from wave to floating structure or to methods of converting the motion of a floating structure to useful power. The prior art does not make allowance for the random character of the incident waves by matching floating structure response to wave conditions that vary (1) annually for different locations around the world, (2) monthly (seasonal) fluctuations, and (3) over short intervals of time varying from fractions of an incident wave period to over several wave periods. Further, the prior art does not match the power train impedance to the incident wave characteristics so as to optimize power absorption and short time energy storage to achieve maximum power train efficiency.
The prior art does not analyze the economic factors that must be considered for an energy system to provide base load power to a shore installation. For example, the selection of deployment site includes factors such as bathymetry conditions for mooring and power transmission, distance from shore, matching onboard power generation to shore side power grid specifications, mooring depth, power collection from individual wave energy generating units, and power conditioning and transmission to shore.
It is an object of the present invention to overcome the deficiencies of the prior art and provide a wave driven power generation system which efficiently converts wave energy into electrical energy and which is cost effective to construct and maintain.
Other objects and advantages of the invention will appear from the following description.